1. Field of the Invention
The present invention relates generally to a head of a hot melt type inkjet printer, and more particularly to a sheet shaped heating device used for a head of a hot melt type inkiet printer.
2. Description of the Related Art
A hot melt type inkiet head has a plurality of nozzle heads corresponding to a plurality of colors of inks actually used for printing, respectively. Each of the nozzle heads has a large number of nozzle holes. In such a hot melt type inkiet head, when printing, solid hot melt inks are melted by heat, and then, the hot melt inks in the liquid state are ejected through the nozzle holes. Therefore, it is necessary to heat up the inks quickly at the start of printing, and keep temperature of the inks at a predetermined high temperature during printing. Here, a performance of an ink ejection is sensitively changed with temperature of inks. If temperature of each nozzle head is not uniform, ejection speed of inks irregularly varies. As a result, printing quality is reduced. Therefore, in order to enhance the printing quality, it is necessary to apply heat to each nozzle head suitably, and that an optimum temperature distribution is set for each nozzle head. In order to apply heat to each nozzle head, the hot melt type inkjet head has a sheet shaped heater.
A sheet shaped heater is typically used as a heater for the hot melt type inkiet head. The sheet shaped heater has an insulating sheet made of polyimide or the like. On the insulating sheet, a meandering wiring pattern is formed. Width and length of the wire of the wiring pattern are designed so as to set a certain wattage density in each part of the wire. The sheet shaped heater is attached near the nozzle heads, and applies heat to the nozzle heads in order to set an optimum temperature distribution for each nozzle head. More concretely, the sheet shaped heater is bonded to a mounting part of the inkiet head located near the nozzle heads by using an adhesive etc., in a condition that a surface of the sheet shaped heater abuts a surface of the mounting part. Therefore, heat generated by the wiring pattern of the sheet shaped heater is conduct to the nozzle head through the mounting part.
However, the surface of the mounting part is flat and relatively hard, whereas the surface of the sheet shaped heater is easy to curve, since the insulating sheet made of polyimide or the like is soft and flexible. In case that the surface of the sheet shaped heater has curved and a concave portion has been formed on it, if the surface of the sheet shaped heater is bonded to the surface of the mounting part, an enclosed space is formed between them, and air is confined in the enclosed space.
Furthermore, if the enclose space is formed in the vicinity of the middle of the surface of the sheet shaped heater, it is difficult to remove the air and the enclosed space.
Moreover, if the enclosed space has been formed, the surface of the sheet shaped heater is partially separate from the surface of the mounting part. Hence, heat generated by the wiring pattern is not completely conducted to the nozzle head through the mounting part. Accordingly, thermal efficiency is reduced, a temperature distribution is dispersed, and printing quality is reduced.